So-called nanoparticles having an average particle size of less than 1 μm and nanoparticle dispersion liquids containing the nanoparticles dispersed therein have been subjected to various studies in various fields such as the fields of biotechnology, genetic engineering, immunology, medical treatment, environment, and electronic devices.
For example, a dispersion liquid which includes an LnOX (Ln represents a rare earth element and X represents a halogen element) nanoparticle having an average particle size of from one to 800 nm dispersed in a solvent having a high salt concentration (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2009-138081) has been known.
A dispersion liquid which includes a Y2O3 nanoparticle dispersed in a K3PO4-containing solvent (for example, see Journal of Physics: Conference Series 191 (2009): 012003-1-012003-7) has been also known.